In the processes known in the art for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using a medium pore shape selective acid crystalline zeolite, such as ZSM-5 type catalyst, process conditions can be varied to favor the formation of hydrocarbons of varying molecular weight. At moderate temperature and relatively high pressure, the conversion conditions favor C.sub.10 + aliphatic product. Lower olefinic feedstocks containing C.sub.2 -C.sub.8 alkenes may be converted. A typical reactive feedstock consists essentially of C.sub.3 -C.sub.6 mono-olefins, with varying amounts of nonreactive paraffins and the like being acceptable components.
U.S. Pat. Nos. 4,520,221, 4,568,786 and 4,658,079 to C. S. H. Chen et al., incorporated herein by reference in their entirety, disclose further advances in zeolite catalyzed olefin oligomerization. These patents disclose processes for the oligomerization of light, or lower, olefins using zeolite catalyst such as ZSM-5. The oligomers so produced are near linear in structure and contain internal olefin unsaturation. These unique olefinic oligomers are produced by surface deactivation of the ZSM-5 type catalyst by pretreatment with a surface-neutralizing base. The processes of Chen et al. provide a particularly useful means to prepare slightly branched higher olefinic hydrocarbons from inexpensive lower olefins, particularly propylene.
In U.S. Pat. No. 4,962,249, near linear higher olefinic hydrocarbons produced by the oligomerization of lower olefins using surface deactivated zeolite catalyst are converted to a mixture comprising slightly branched and linear higher alpha olefins. These alpha olefins are oligomerized to lubricant grade hydrocarbons in contact with cationic, Ziegler or coordination catalyst. Oligomerization of the aforementioned alpha olefins using reduced valence state Group VIB metal oxide catalyst on porous support provides a hydrocarbon lubricant with a viscosity index of greater than 130 at 100.degree. C. Olefin metathesis with ethene, as described in Olefin Metathesis by K. J. Ivin, published by Academic Press, Chapter 5, is applied to the internal olefinic oligomers of Chen et al. to provide a route to the alpha olefins suitable for the production of synthetic lubricants, utilizing the process described in U.S. Pat. Nos. 4,827,064 and 4,827,073 to M. Wu, incorporated herein by reference. The lubricants recovered comprise the 650.degree. F.+ (343.degree. C.+) fraction of the oligomerization reaction product.
It is an object of the present invention to provide a process for the co-production of high VI synthetic lubricants and high cetane value fuel from slightly branched higher internal olefins.
It is another object of the present invention to provide a process for the production of high cetane value fuel from slightly branched hydrocarbon oligomers.
A further object of the present invention is to provide a process for the oligomerization of inexpensive light olefins to slightly branched olefins for the direct co-production of synthetic lubricants and high cetane fuel.